BANK 2 MISFIRING

I replaced my valve cover gaskets this past summer because of oil leaking into the plug wells. I recently replaced all 8 spark plugs as well. Using the Peake code reader, the codes I am getting are " misfire detected, cyl. 5" & cyl 6, 7 & 8. Additionally, there is a " random or unknown cylinder" misfire along with " catalyst damaging" on cyl 5, 6, 7 & 8. I've swapped the ignition coils & the misfires are still on cyl 5 - 8. Also, the pre-cat O2 sensors were replaced about a year ago.

The check engine light flashes during wide open throttle beyond 3000 rpm & it struggles to rev past 4000 rpm - I took my foot off the accelerator after a while, thinking that I might do more damage if I tried to push it beyond 4000 rpms.

A flashing check engine light is not good. It indicates cat damage is occuring. Tell me all that has been done to the car, I need to know if the intake manifold has been off and if the PCV plate is original.

The intake manifold hasn't been off & the PCV plate is original. I'm assuming that the PCV is the same thing as the CCV? Do I need to replace the vacuum lines & rear intake manifold gaskets? How much time is required for a weekend mechanic to do this?